Unit 3 - Organisms exchange substances with their environment

Question 1

What are the 3 main factors that affect the rate of diffusion?

Answer 1

surface area, concentration gradient, diffusion distance

Question 2

How are the gills adapted to increase the rate of diffusion?

Answer 2

large surface area- many lamellae in gill filaments
short diffusion distance- lamellae are thin, surface of cells close to blood capillaries
Concentration gradient- counter current system

Question 3

What is the counter current system?

Answer 3

blood and water flow in opposite directions to maintain a concentration gradient across the whole length of the gill

Question 4

What do the spiracles do?

Answer 4

allow oxygen to diffuse into insects, open and close to restrict water loss

Question 5

How are insects adapted for efficient gas exchange?

Answer 5

large surface area- trachea branches into lots of tracheoles
short diffusion distance- tracheoles have thin permeable walls in contact with muscle cells
concentration gradient- respiration uses oxygen maintaining concentration gradient

Question 6

How are insects adapted to reduce water loss?

Answer 6

spiracles open and close, hairs to trap water, exoskeleton is waterproof, chitin

Question 7

What are the two types of leaf ?

Answer 7

dicotylendous and xerophytic

Question 8

What is the equation for stomatal density?

Answer 8

stomatal density = number of stomata / area

Question 9

How are dicotylendous plants adapted for gas exchange?

Answer 9

large surface area: air spaces in spongy mesophyll
concentration gradient: carbon dioxide is used in photosynthesis
short diffusion distance: thin plant tissues and stomata
lots of stomata

Question 10

How are xerophytic plants adapted to reduce water loss?

Answer 10

• fewer stomata
• thick waxy cuticle increases diffusion distance and reduces evaporation
• stomata open and close
• fine hairs to trap moist air
• sunken stomata so traps water vapour and decreases water potential

Question 11

How are the alveoli adapted for efficient gas exchange?

Answer 11

• rich network of blood capillaries to maintain a steep concentration gradient
• alveolar epithelium are one cell thick so short diffusion distance
• alveolar epithelium are permeable so surface is always moist
• air in the alveoli is saturated with water vapour to reduce the rate of water loss

Question 12

What happens during inspiration?

Answer 12

• diaphragm contracts and flattens
• external intercostal muscles contract
• ribs move up and out
• volume increases, pressure decreases
• air flows into the lungs down the pressure gradient

Question 13

What happens during expiration?

Answer 13

• diaphragm relaxes and domes
• external intercostal muscles relax
• ribs move down and out
• volume increases, pressure decreases
• air flows out of the lungs down the pressure gradient

Question 14

What are the two types of peptidases?

Answer 14

exopeptidase and endopeptidase

Question 15

What do exopeptidase do?

Answer 15

hydrolyse peptide bonds at the ends of the protein removing a single amino acid

Question 16

What do endopeptidases do?

Answer 16

hydrolyse peptide bonds within a protein

Question 17

What are dipeptidases?

Answer 17

exopeptidases that work specifically on dipeptides

Question 18

Where are dipeptidases found?

Answer 18

cell-surface membrane of the epithelial cells in the small intestine

Question 19

How is lactose digested?

Answer 19

epithelial cells in the small intestine secrete lactase which hydrolyses lactose into glucose + galactose by breaking glycosidic bonds

Question 20

How is starch hydrolysed into maltose?

Answer 20

salivary glands release amylase, amylase hydrolyses starch into maltose by breaking the glycosidic bonds. pancreas also produces amylase.

Question 21

How is maltose hydrolysed into alpha glucose?

Answer 21

epithelial cells of the small intestine secrets maltase which hydrolyses maltose into alpha glucose.

Question 22

How is glucose absorbed?

Answer 22

absorbed by facilitated diffusion and co-transport in the ileum

Question 23

What is the role of bile?

Answer 23

to emulsify large lipid molecules into smaller lipid molecules increasing the surface area

Question 24

How are lipids hydrolysed?

Answer 24

lipase hydrolyses the ester bonds of small lipid molecules into monoglycerides and fatty acids

Question 25

How are monoglycerides and fatty acids absorbed?

Answer 25

bile salts sticks to monoglycerides on the fatty acids to make micelles. micelles allow monoglycerides and fatty acids to be taken up by simple diffusion as they are lipid soluble

Question 26

What are adaptations of the xylem?

Answer 26

vessels with no end walls, dead and hollow, thick lignin walls, pits in walls

Question 27

What is the function of lignin?

Answer 27

waterproofs cells, strengthens and supports the vessels, forms patterns (allows flexibility), prevents the xylem vessels from collapsing

Question 28

Why are there pits in the walls of the xylem?

Answer 28

to allow for lateral movement of water

Question 29

What is cohesion?

Answer 29

tendency of water molecules to stick together, hydrogen bonds allows water to have high cohesive forces

Question 30

What is the cytoplasmic pathway?

Answer 30

Mesophyll cells have a lower potential due to the evaporation
of water. Water enters via osmosis from neighbouring cells.

Question 31

Describe the mass flow theory

Answer 31

• sucrose actively transported into phloem
• by companion cells
• lowers water potential and water enters by osmosis
• creates hydrostatic pressure
  -mass flow to respiring cells
• unloaded by active transport

Question 32

Describe the cohesion-tension theory

Answer 32

• water evaporates from cells and leaves the plant through the stomata
• this creates tension
• cohesion results in water forming a continuous column in the stem
• tension means that water column is pulled up the xylem towards the stomata in the transpiration pull

Question 33

What are capillaries made up of?

Answer 33

endothelium cells

Question 34

How is tissue fluid formed?

Answer 34

-left ventricle creates high blood pressure
- at the capillaries there is high hydrostatic pressure
- the high pressure forces water, aa, glucose through the pores into the capillary endothelium
- this forms the tissue fluid

Question 35

How are waste products transported back into the blood?

Answer 35

• large proteins/ cells remain in the blood plasma
• this lowers the water potential in the plasma
• water moves from the tissue fluid into the plasma by osmosis, down the water potential gradient
• this will carry CO2, urea back into the blood
• excess tissue fluid drains into the lymphatic system

Question 36

Describe the structure of haemoglobin

Answer 36

four polypeptide chains each carrying a heam group

Question 37

Describe the role of haemoglobin?

Answer 37

oxygen molecules bind to the haem groups and are transported to respiring tissues

Question 38

How does partial pressure of oxygen affect oxygen-haemoglobin binding?

Answer 38

as ppO2 increases, the affinity for oxygen on haemoglobin increases, so oxygen binds to haemoglobin. when ppO2 is low, oxygen dissociates from haemglobin

Question 39

How does ppCO2 affect oxygen-haemoglobin binding?

Answer 39

as ppCO2 increases, the pH becomes acidic causing haemoglobin to change shape. affinity for oxygen of haemoglobin decreases, so oxygen dissociates from haemoglobin

Question 40

How does saturation of haemoglobin with oxygen affect oxygen-haemoglobin binding?

Answer 40

it is hard for the first oxygen molecule to bind. once it does, it changes the shape to make it easier for the second and third molecules to bind. it is slightly harder for the fourth oxygen molecule to bind and it is more saturated

Question 41

How does carbon dioxide affect the position of an oxyhaemoglobin dissociation curve?

Answer 41

curve shifts to the right because heamoglobin’s affinity for oxygen has decreased

Question 42

Structure of arteries

Answer 42

thick walls to handle high pressures, muscular and elastic to control blood flow

Question 43

Structure of veins

Answer 43

thin walls as lower pressure, valves to prevent backflow of blood